This invention relates to a peptide immunogen comprising a novel artificial T helper cell epitope (Th) covalently linked to a desired target antigenic site comprising B cell epitopes and optionally a general immune stimulator sequence. The artificial Th epitope imparts to the peptide immunogen the capability to induce strong T helper cell-mediated immune responses and the production of antibodies directed against the xe2x80x9ctarget antigenic site.xe2x80x9d The invention also provides for the advantageous replacement of carrier proteins and pathogen-derived T helper cell sites in established peptide immunogens by the novel artificial T helper cell epitopes for improved immunogenicity.
Many rules have been developed for predicting the amino acid sequences of T cell epitopes. However, because there is no central unifying theory on how or what makes a particular amino acid sequence useful as a T cell epitope, the rules are empirical and are not universally applicable. Being aware of these rules, the novel artificial T helper cell epitopes of the present invention were developed, nevertheless, by empirical research.
The peptide immunogens of the present invention are useful for evoking antibody responses in an immunized host to a desired target antigenic site, including sites taken from pathogenic organisms, and sites taken from normally immunosilent self-antigens and tumor-associated targets. Accordingly, the peptides of the invention are useful in diverse medical and veterinary applications, such as: vaccines to provide protective immunity from infectious disease; immunotherapies for treating disorders resulting from malfunctioning normal physiological processes; immunotherapies for treating cancer and as agents to intervene in normal physiological processes to produce desirable results.
For example, the novel artificial T helper cell epitopes of the present invention provide novel short peptide immunogens that elicit antibodies targeted to luteinizing hormone-releasing hormone (LHRH) and are useful for contraception, control of hormone-dependent tumors, prevention of boar taint, and immunocastration. The novel artificial Th epitopes of the present invention have been found to provoke an immune response when combined with target B cell epitopes of various microorganisms/proteins/peptides. In addition to LHRH, the artificial Th epitopes of the present invention have been found to be useful when linked to other target antigenic sites including somatostatin for growth promotion in farm animals; IgE for treatment of allergy; the CD4 receptor of T helper cells for treatment and prevention of HIV infection and immune disorders; foot-and-mouth disease virus capsid protein for prevention of foot-and-mouth disease; HIV virion epitopes for prevention and treatment of HIV infection; the circumsporozoite antigen of Plasmodium falciparum for prevention and treatment of malaria; and Cholesteryl ester transport protein (CETP) for prevention and treatment of arteriosclerosis.
It is known that most antibody immune responses are cell-mediated, requiring cooperative interaction between antigen-presenting cells, B cells (antibody-producing cells which also function as antigen-presenting cells), and T helper (Th) cells. Consequently, the elicitation of an effective antibody response requires that the B cells recognize the target antigenic site (B cell epitope) of a subject immunogen and the T helper cells recognize a Th epitope. Generally, the T helper epitope on a subject immunogen is different from its B cell epitope(s) (Babbitt et al., Nature, 1985; 317: 359-361). The B cell epitope is a site on the desired target recognized by B cells which in response produce antibodies to the desired target site. It is understood that the natural conformation of the target determines the site to which the antibody directly binds. The T helper cell recognition of proteins is, however, much more complex and less well understood. (Cornette et al., in Methods in Enzymology, vol 178, Academic Press, 1989, pp 611-634).
Under present theories, evocation of a Th cell response requires the T helper cell receptor to recognize not the desired target but a complex on the membrane of the antigen-presenting cell formed between a processed peptide fragment of the target protein and an associated class II major histocompatibility complex (MHC). Thus, peptide processing of the target protein and a three-way recognition is required for the T helper cell response. The three part complex is particularly difficult to define since the critical MHC class II contact residues are variably positioned within different MHC binding peptides (Th epitopes) and these peptides are of variable lengths with different amino acid sequences (Rudensky et al., Nature, 1991; 353:622-627). Furthermore, the MHC class II molecules themselves are highly diverse depending on the genetic make-up of the host. The immune responsiveness to a particular Th epitope is thus in part determined by the MHC genes of the host. In fact, it has been shown that certain peptides only bind to the products of particular class II MHC alleles. Thus, it is difficult to identify promiscuous Th epitopes, i.e., those that are reactive across species and across individuals of a single species. It has been found that the reactivity of Th epitopes is different even among individuals of a population.
The multiple and varied factors for each of the component steps of T cell recognition: the appropriate peptide processing by the antigen-processing cell, the presentation of the peptide by a genetically determined class II MHC molecule, and the recognition of the MHC molecule/peptide complex by the receptor on T helper cells have made it difficult to determine the requirements for promiscuous Th epitopes that provide for broad responsiveness (Bianchi et al., EP 0427347; Sinigaglia et al., chapter 6 in Immunological Recognition of Peptides in Medicine and Biology, ed., Zegers et al., CRC Press, 1995, pp 79-87).
It is clear that for the induction of antibodies, the immunogen must comprise both the B cell determinant and Th cell determinant(s). Commonly, to increase the immunogenicity of a target, the Th response is provided by coupling the target to a carrier protein. The disadvantages of this technique are many. It is difficult to manufacture well-defined, safe, and effective peptide-carrier protein conjugates for the following reasons:
1. Chemical coupling are random reactions introducing heterogeneity of size and composition, e.g., conjugation with glutataraldehyde (Borras-Cuesta et al., Eur J Immunol, 1987; 17: 1213-1215);
2. the carrier protein introduces a potential for undesirable immune responses such as allergic and autoimmune reactions (Bixler et al., WO 89/06974);
3. the large peptide-carrier protein elicits irrelevant immune responses predominantly misdirected to the carrier protein rather than the target site (Cease et al., Proc Natl Acad Sci USA, 1987; 84: 4249-4253); and
4. the carrier protein also introduces a potential for epitopic suppression in a host which had previously been immunized with an immunogen comprising the same carrier protein. When a host is subsequently immunized with another immunogen wherein the same carrier protein is coupled to a different hapten, the resultant immune response is enhanced for the carrier protein but inhibited for the hapten (Schutze et al., J Immunol, 1985; 135: 2319-2322).
To avoid these risks, it is desirable to replace the carrier proteins. T cell help may be supplied to a target antigen peptide by covalent binding to a well-characterized promiscuous Th determinant. Known promiscuous Th are derived from the potent pathogenic agents such as measles virus F protein (Greenstein et al., J Immunol, 1992; 148: 3970-3977) and hepatitis B virus surface antigen (Partidos et al., J Gen Virol 1991; 72: 1293-1299). The present inventors have shown that many of the known promiscuous Th are effective in potentiating a poorly immunogenic peptide, such as the decapeptide hormone luteinizing hormone-releasing hormone (LHRH) (U.S. Pat. No. 5,759,551). Other chimeric peptides comprising known promiscuous Th epitopes with poorly immunogenic synthetic peptides to generate potent immunogens have been developed (Borras-Cuesta et al., 1987). Well-designed promiscuous Th/B cell epitope chimeric peptides are capable of eliciting Th responses with resultant antibody responses targeted to the B cell site in most members of a genetically diverse population (U.S. Pat. No. 5,759,551).
A review of the known promiscuous Th epitopes shows that they range in size from approximately 15 to 50 amino acid residues (U.S. Pat. No. 5,759,551) and often share common structural features with specific landmark sequences. For example, a common feature is the presence of amphipathic helices. These are alpha-helical structures with hydrophobic amino acid residues dominating one face of the helix and charged and polar resides dominating the surrounding faces (Cease et al., 1987). Known promiscuous Th epitopes also frequently contain additional primary amino acid patterns such as a charged residue, -Gly-, followed by two to three hydrophobic residues, followed in turn by a charged or polar residue (Rothbard and Taylor, EMBO J, 1988; 7:93-101). Th epitopes with this pattern are called Rothbard sequences. It has also been found that promiscuous Th epitopes often obey the 1, 4, 5, 8 rule, where a positively charged residue is followed by hydrophobic residues at the fourth, fifth and eighth positions, consistent with an amphipathic helix having positions 1, 4, 5 and 8 located on the same face. This pattern of hydrophobic and charged and polar amino acids may be repeated within a single Th epitope (Partidos et al., J Gen Virol, 1991; 72:1293-99). Most, if not all, of the known promiscuous T cell epitopes contain at least one of the periodicities described above.
Promiscuous Th epitopes derived from pathogens include the hepatitis B surface and core antigen helper T cell epitopes (HBsAg Th and HBc Th), the pertussis toxin helper T cell epitopes (PT Th), the tetanus toxin helper T cell epitopes (TT Th), the measles virus F protein helper T cell epitopes (MVF Th), the Chlamydia trachomatis major outer membrane protein helper T cell epitopes (CT Th), the diphtheria toxin helper T cell epitopes (DT Th), the Plasmodium falciparum circumsporozoite helper T cell epitopes (PF Th), the Schistosoma mansoni triose phosphate isomerase helper T cell epitopes (SM Th), and the Escherichia coli TraT helper T cell epitopes (TraT Th). The sequences of these pathogen-derived Th epitopes can be found in U.S. Pat. No. 5,759,551 as SEQ ID NOS:2-9 and 42-52 therein, incorporated herein by reference; in Stagg et al., Immunology, 1993; 79;1-9; and in Ferrari et al., J Clin Invest, 1991; 88: 214-222, also incorporated by reference
The use of such pathogen-derived sites for the immuno-potentiation of peptide B cell sites for application to LHRH has been described in U.S. Pat. No. 5,759,551, for HIV in Greenstein et al. (1992), for malaria in EP 0 427,347, for rotavirus in Borras-Cuesta et al. (1987), and for measles in Partidos et al. (1991).
Useful Th epitopes may also include combinatorial Th epitopes. In Wang et al. (WO 95/11998), a particular class of combinatorial Th epitopes, a xe2x80x9cStructured Synthetic Antigen Libraryxe2x80x9d (SSAL) was described. Th SSAL epitopes comprise a multitude of Th epitopes with amino acid sequences organized around a structural framework of invariant residues with substitutions at specific positions. The sequences of the SSAL are determined by retaining relatively invariant residues while varying other residues to provide recognition of the diverse MHC restriction elements. This may be accomplished by aligning the primary amino acid sequence of a promiscuous Th, selecting and retaining as the skeletal framework the residues responsible for the unique structure of the Th peptide, and varying the remaining residues in accordance with known MHC restriction elements. Lists of the invariant and variable positions with the preferred amino acids of MHC restriction elements are available to obtain MHC-binding motifs. These may be consulted in designing SSAL Th epitopes (Meister et al., Vaccine, 1995; 13:581-591).
The members of the SSAL may be produced simultaneously in a single solid-phase peptide synthesis in tandem with the targeted B cell epitope and other sequences. The Th epitope library sequences are designed to maintain the structural motifs of a promiscuous Th epitope and at the same time, accommodate reactivity to a wider range of haplotypes. For example, the degenerate Th epitope xe2x80x9cSSAL1 TH1xe2x80x9d (WO 95/11998), was modeled after a promiscuous epitope taken from the F protein of the measles virus (Partidos et al., 1991). SSAL1 TH1 was designed to be used in tandem with a target antigen, LHRH. Like the measles epitope from which it was derived, SSAL1 TH1 was designed to follow the Rothbard sequence and the 1, 4, 5, 8 rules and is a mixture of four peptides:
A charged residue Glu or Asp is added at position 1 to increase the charge surrounding the hydrophobic face of the Th. The hydrophobic face of the amphipathic helix is then maintained by hydrophobic residues at 2, 5, 8, 9, 10, 13 and 16. Positions at 2, 5, 8, 9, 10, and 13 are varied to provide a facade with the capability of binding to a wide range of MHC restriction elements. The net effect of the SSAL feature is to enlarge the range of immune responsiveness of the artificial Th (WO 95/11998).
Other attempts have been made to design xe2x80x9cidealizedxe2x80x9d artificial Th epitopesxe2x80x9d incorporating all of the properties and features of known promiscuous Th epitopes. Several peptide immunogens comprising these artificial promiscuous Th epitopes, including those in the form of SSAL, have also been constructed. The artificial Th sites have been combined with peptide sequences taken from self-antigens and foreign antigens to provide enhanced antibody responses to sitexe2x80x94specific targets (WO 95/11998; Alexander et al., Immunity, 1994, 1:751; Del Guerio et al., Vaccine, 1997, 15:441) that have been described as highly effective. Such peptide immunogens are preferred for providing effective and safe antibody responses, and for their immunopotency, arising from a broadly reactive responsiveness imparted by the idealized promiscuous Th sites described.
The present invention provides an immunogenic peptide composition comprising a promiscuous artificial T helper cell epitope linked to a synthetic peptide B cell epitope or xe2x80x9ctarget antigenic sitexe2x80x9d. The immunogenic peptide comprise an artificial T helper cell (Th) epitopes and a target antigenic site containing B cell epitopes and, optionally, a general immune stimulator sequence. The presence of an artificial Th epitope in the immunogenic peptide impart thereto a capability to induce a strong T helper cell-mediated immune response with the production of a high level of antibodies directed against the xe2x80x9ctarget antigenic site.xe2x80x9d The present invention further provides for the advantageous replacement of carrier proteins and pathogen-derived T helper cell sites in established peptide immunogens with artificial T helper cell epitopes designed specifically to improve their immunogenicity. The novel short peptide immunogens with the artificial Th epitopes of the present invention elicit a high level of antibodies targeted to luteinizing hormone-releasing hormone (LHRH) useful for contraception, the control of hormone-dependent tumors, the prevention of boar taint, and immunocastration.
The artificial Th epitopes were developed empirically, mindful of the known rules for predicting promiscuous T cell epitopes. In the absence of a unifying theory explaining the mechanism of Th epitopes, these xe2x80x9cpredicativexe2x80x9d rules serve merely as guidelines for designing effective artificial Th epitopes. The artificial Th epitopes of the present invention have been found to be useful when linked to target antigenic sites and optionally with a immunostimulatory sequence. The immunogenic peptides of the present invention may be represented by the formulae:
(A)n-(Target antigenic site)-(B)o-(Th)m-X 
or
(A)n-(B)o-(Th)m-(B)o-(Target antigenic site)-X 
or
(A)n-(Th)m-(B)o-(Target antigenic site)-X 
or
(Target antigenic site)-(B)o-(Th)m-(A)n-X 
or
(Th)m-(B)o-(Target antigenic site)-(A)n-X 
wherein:
A is an amino acid or a general immunostimulatory sequence, e.g., the invasin domain (Inv) (SEQ ID NO:78) where n is more than one, the individual A""s may be the same or different;
B is selected from the group consisting of amino acids, xe2x80x94NHCH (X) CH2SCH2COxe2x80x94, xe2x80x94NHCH (X) CH2SCH2CO (xe2x96xa1N) Lys-, xe2x80x94NHCH (X) CH2S-succinimidyl (xe2x96xa1N) Lys-, and xe2x80x94NHCH (X) CH2S-(succinimidyl)-;
Th is an artificial helper T cell epitope selected from the group consisting of SEQ ID NOS:6-22, 31-35 and 105 and an analog or segment thereof;
xe2x80x9cTarget antigenic sitexe2x80x9d is a desired B cell epitope, a peptide hapten, or an immunologically reactive analog thereof;
X is an aminoacid xcex1-COOH, xe2x80x94CONH2;
n is from 1 to about 10;
m is from 1 to about 4; and
o is from 0 to about 10.
An example of a peptide hapten as a target antigenic site is LHRH (SEQ ID NO: 77).
The compositions of the present invention comprise peptides capable of evoking antibody responses in an immunized host to a desired target antigenic site. The target antigenic site may be derived from pathogenic organisms and normally immunosilent self-antigens and tumor-associated targets such as LHRH.
Accordingly, the compositions of the present invention are useful in many diverse medical and veterinary applications. These include vaccines to provide protective immunity from infectious disease, immunotherapies for the treatment of disorders resulting from the malfunction of normal physiological processes, immunotherapies for the treatment of cancer, and agents to desirably intervene in and modify normal physiological processes.
Some of the targets antigens which may be covalently linked to the Th epitopes of the present invention include: LHRH for contraception, the control of hormone dependent tumors and immunocastration; somatostatin for growth promotion in farm animals; IgE for treatment of allergy; the CD4 receptor of T helper cells for treatment and prevention of HIV infection and immune disorders; foot-and-mouth disease virus capsid protein as a vaccine for the prevention of foot-and-mouth disease; the CS antigen of Plasmodium for prevention of malaria; CETP for prevention and treatment of arteriosclerosis; and HIV virion epitopes for prevention and treatment of HIV infection.
Idealized artificial Th epitopes have been provided. These are modeled on two known natural Th epitopes and SSAL peptide prototypes, disclosed in WO 95/11998. The SSALS incorporate combinatorial MHC molecule binding motifs (Meister et al., 1995) intended to elicit broad immune responses among the members of a genetically diverse population. The SSAL peptide prototypes were designed based on the Th epitopes of the measles virus and hepatitis B virus antigens, modified by introducing multiple MHC-binding motifs. The design of the other Th epitopes were modeled after other known Th epitopes by simplifying, adding, and/or modifying, multiple MHC-binding motifs to produce a series of novel artificial Th epitopes. The newly adapted promiscuous artificial Th sites were incorporated into synthetic peptide immunogens bearing a variety of target antigenic sites. The resulting chimeric peptides were able to stimulate effective antibody responses to the target antigenic sites.
The prototype artificial helper T cell (Th) epitope shown in Table 1a as xe2x80x9cSSAL1 TH1xe2x80x9d, a mixture of four peptides (SEQ ID NOS:2, 3, 4, 5) is an idealized Th epitope modeled from a promiscuous Th epitope of the F protein of measles virus (Partidos et al. 1991). The model Th epitope, shown in Table 1a as xe2x80x9cMVF Thxe2x80x9d (SEQ ID NO:1) corresponds to residues 288-302 of the measles virus F protein. MVF Th (SEQ ID NO:1) was modified to the SSAL1 Th1 prototype (SEQ ID NOs:2, 3, 4, 5) by adding a charged residue Glu/Asp at position 1 to increase the charge surrounding the hydrophobic face of the epitope; adding or retaining a charged residues or Gly at positions 4, 6, 12 and 14; and adding or retaining a charged residue or Gly at positions 7 and 11 in accordance with the xe2x80x9cRothbard Rulexe2x80x9d. The hydrophobic face of the Th epitope comprise residues at positions 2, 5, 8, 9, 10, 13 and 16. Hydrophobic residues commonly associated with promiscuous epitopes were substituted at these positions to provide the combinatorial Th SSAL epitopes, SSAL1 Th1 (SEQ ID NOs:2, 3, 4, 5). The hydrophobic residues conforming to the Rothbard sequence rule are shown in bold (Table 1a, SEQ ID NO:1). Positions in the sequence obeying the 1, 4, 5, 8 rule are underlined. Another significant feature of the prototype SSAL1 Th1 (SEQ ID NOS:2, 3, 4, 5) is that positions 1 and 4 is imperfectly repeated as a palindrome on either side of position 9, to mimic an MHC-binding motif. This xe2x80x9c1, 4, 9xe2x80x9d palindromic pattern of SSAL1 Th1 was further modified in SEQ ID NO:3 (Table 1a) to more closely reflect the sequence of the original MVF model Th (SEQ ID NOs:1). Also, the hydrophobicity of the SSAL1 Th1 prototype (SEQ ID NOs:2, 3, 4, 5) was modulated in SEQ ID NOS:6, 7, and 8 by the addition of methionine residues at variable positions 1, 12, and 14. Experimental data shows that SEQ ID NOS:6, 7, 8 coupled to a target antigenic site enhanced the antibody response in the immunized animals to the target antigenic site.
SEQ ID NOS:6, 7, 8 was simplified to SEQ ID NOS:6, 9, 10 and 11 (Table 1a) to provide further immunogenic SSAL Th epitopes. SEQ ID NOS:6, 7, 8 was further simplified to SEQ ID NOS:6, 12-14 (Table 1a) to provide a series of single-sequence epitopes. SSAL Th SEQ ID NOS:4, 9, 10 and 11 and the single sequence Th epitopes SEQ ID NOS:6, 12-14, coupled to target antigenic sites also provided enhanced immunogenicity
It was found that the immunogenicity of SEQ ID NOS:6, 7, 8 may be improved by extending the N terminus with a non-polar and a polar uncharged amino acid, e.g., Ile and Ser, and extending the C terminus by a charged and hydrophobic amino acid, e.g., Lys and Phe. This is shown in Table 1a as SEQ ID NO:15, 16 and 17 from which simplified SSAL Th epitopes SEQ ID NOS:15 and 18, 105 and 19 were derived. Peptide immunogens comprising a target antigenic site and a Th epitope selected from SEQ ID NOS:15-17, 15 and 18, 105 and 19, and 123 and 124 displayed enhanced immunogenicity. Single-sequence peptides such as SEQ ID NOS:15, 20-22 were also synthesized and tested for immunogenicity in animals. These were also found to be effective Th epitopes.
The SSAL artificial helper epitope shown in Table 1b as xe2x80x9cSSAL2 Th2xe2x80x9d (SEQ ID NOS:26-30) was modeled after a promiscuous epitope from the hepatitis B virus surface antigen SEQ ID NO:23 corresponding to residues 19-33 of the hepatitis B surface antigen (HBsAg) (Greenstein et al. 1992). The pathogen-derived model Th, was modified to SEQ ID NO:24 by adding three Lysines to improve solubility in water; the C-terminal Asp was deleted in SEQ ID NO:25 to facilitate the synthesis of chimeric peptides wherein Gly-Gly was introduced as spacers. The SSAL2 Th2 (SEQ ID NOs:26-30) was further modified from SEQ ID NO:24 by varying the positively charged residues therein at positions 1, 2, 3 and 5 to vary the charge surrounding the hydrophobic face of the helical structure. A charged amino acid at variable position 3 also contributed a required residue to generate the idealized Th epitope, SSAL2 Th2 (SEQ ID NOS:26-30), which obeyed the 1, 4, 5, 8 rule (underlined residues). The hydrophobic face of the amphipathic helix consists of hydrophobic residues at positions 4, 6, 7, 10, 11, 13, 15 and 17 of SEQ ID NOS:26-30. The Rothbard sequence residues are shown in bold for prototype SSAL2 Th2 (SEQ ID NOS:26-30).
SEQ ID NOS:31-35 were simplified from the idealized SSAL2 Th2 prototype (SEQ ID NOS:26-30) as described above. For example, variable hydrophobic residues were replaced with single amino acids, such as Ile or Met (SEQ ID NOS:31-35). The hydrophobic Phe in position 4 was incorporated as a feature of SEQ ID NO:34 while deleting the three lysines. The deletion of the C-terminal Asp was incorporated as a feature of SEQ ID NOS:32, 34, and 35. Further modifications included the substitution of the C-termini by a common MHC-binding motif AxTxIL (Meister et al, 1995).
Each of the novel artificial Th epitopes, SEQ ID NOS:6, 12-19, 105, 123, 124 20-22 and 31-35 were coupled to a variety of target antigenic sites to provide peptide immunogens. The target antigenic sites include the peptide hormones, LHRH and somatostatin, B cell epitopes from immunoglobulin IgE, the T cell CD4 receptor, the VP1 capsid protein of foot-and-mouth disease virus; the CS antigen of Plasmodium falciparum; and cholesteryl ester transport protein (CETP); and B cell epitopes from HIV. The results show that effective anti-target site antibodies cross-reactive with a diverse group of self-antigens and foreign antigens were produced. Most important, the antibody responses were directed to the target antigenic sites and not to the novel Th epitopes. The results for the novel peptide immunogens for LHRH are shown in Tables 2 and 3. The immunogenicity results also show that the antibodies produced were effective against LHRH but not against the Th epitopes themselves. It is to be emphasized that LHRH is a target antigenic site devoid of T cell epitopes (Sad et al., Immunology, 1992; 76: 599-603 and U.S. Pat. No. 5,759,551). Thus, the novel artificial Th epitopes of the present invention represent a new class of promiscuous T helper epitopes.
The artificial Th epitopes of the present invention are contiguous sequences of amino acids (natural or non-natural amino acids) that comprise a class II MHC molecule binding site. They are sufficient to enhance or stimulate an antibody response to the target antigenic site. Since a Th epitope can consist of continuous or discontinuous amino acid segments, not every amino acid of the Th epitope is necessarily involved with MHC recognition. The Th epitopes of the invention further include immunologically functional homologues. Functional Th homologues include immune-enhancing homologues, crossreactive homologues and segments of any of these Th epitopes. Functional Th homologues further include conservative substitutions, additions, deletions and insertions of from one to about 10 amino acid residues and provide the Th-stimulating function of the Th epitope.
The promiscuous Th epitopes of the invention are covalently linked to the N- or C-terminus of the target antigenic site, to produce chimeric Th/B cell site peptide immunogens. The term xe2x80x9cpeptide immunogenxe2x80x9d as used herein refers to molecules which comprise Th epitopes covalently linked to a target antigenic site, whether through conventional peptide bonds so as to form a single larger peptide, or through other forms of covalent linkage, such as a thioester. Accordingly, the Th epitopes (e.g., SEQ ID NOS:6, 12-19, 105, 123, 124, 20-22 and 31-35) are covalently attached to the target antigenic site (e.g., SEQ ID NO:77) either via chemical coupling or via direct synthesis. The Th epitopes may be attached directly to the target site or through a spacer, e.g., Gly-Gly or (xe2x96xa1-N)Lys. In addition to physically separating the Th epitope from the B cell epitope (e.g., SEQ ID NOS:41-64, 71-76, 84-90, 92-94, 96-102, 103, 104, 106, 126-129, and 136-153), the spacer may disrupt any artifactual secondary structures created by the linking of the Th epitope or its functional homologue with the target antigenic site and thereby eliminate any interference with the Th and/or B cell responses. A flexible hinge spacer that enhances separation of the Th and IgE domains can also be useful. Flexible hinge sequences are often proline rich. One particularly useful flexible hinge is provided by the sequence Pro-Pro-Xaa-Pro-Xaa-Pro (SEQ ID NO:79) modeled from the flexible hinge region found in immunoglobulin heavy chains. Xaa therein is any amino acid, preferably aspartic acid. The conformational separation provided by the spacer (See SEQ ID NOS:80 and 82) permits more efficient interactions between the presented peptide immunogen and the appropriate Th cells and B cells. Thus the immune responses to the Th epitope is enhanced to provide improved immune reactivity.
The peptide conjugate immunogens of the invention optionally may also comprise a general immunostimulatory peptide sequence. For example, a domain of an invasin protein (Inv) from the bacteria Yersinia spp (Brett et al., Eur J Immunol, 1993, 23: 1608-1614). This immune stimulatory property results from the capability of this invasin domain to interact with the xcex21 integrin molecules present on T cells, particularly activated immune or memory T cells. A preferred embodiment of the invasin domain (Inv) for linkage to a promiscuous Th epitope has been previously described in U.S. Pat. No. 5,759,551 and is incorporated herein by reference. The said Inv domain has the sequence:
Thr-Ala-Lys-Ser-Lys-Lys-Phe-Pro-Ser-Tyr-Thr-Ala-Thr-Tyr-Gln-Phe xe2x80x83xe2x80x83(SEQ ID NO:78) 
or is an immune stimulatory homologue thereof from the corresponding region in another Yersinia species invasin protein. Such homologues thus may contain substitutions, deletions or insertions of amino acid residues to accommodate strain to strain variation, provided that the homologues retain immune stimulatory properties. The general immunostimulatory sequence may optionally be linked to the Th epitope with a spacer sequence.
The peptide conjugates of this invention, i.e., peptide immunogens which comprise the described artificial Th epitopes, can be represented by the formulas:
(A)n-(Target antigenic site)-(B)o-(Th)m-X 
or
(A)n-(B)o-(Th)m-(B)o-(Target antigenic site)-X 
or
(A)n-(Th)m-(B)o-(Target antigenic site)-X 
or
(Target antigenic site)-(B)o-(Th)m-(A)n-X 
or
(Th)m-(B)o-(Target antigenic site)-(A)n-X 
wherein:
A is optional and is an amino acid or a general immunostimulatory sequence, where N greater than 1, each A may be the same or different;
B is selected from the group consisting of amino acids, xe2x80x94NHCH (X) CH2SCH2COxe2x80x94, xe2x80x94NHCH (X) CH2SCH2CO (xe2x96xa1-N) Lys-, xe2x80x94NHCH (X) CH2S-succinimidyl (xe2x96xa1-N) Lys-, and xe2x80x94NHCH (X) CH2S-(succinimidyl)-;
Th is an artificial helper T cell epitope (SEQ ID NOS:6, 12-19, 105, 20-22 and 31-35) or an immune enhancing homologue or segment thereof;
xe2x80x9cTarget antigenic sitexe2x80x9d is a desired B cell epitope or peptide hapten, or an analog thereof);
X is an amino acid xcex1-COOH OR xe2x80x94COHN2;
n is from 1 to about 10;
m is from 1 to about 4; and
o is from 0 to about 10.
The peptide immunogens of the present invention comprises from about 25 to about 100 amino acid residues, preferably from about 25 to about 80 amino acid residues.
When A is an amino acid, it can be any non-naturally occurring or any naturally occurring amino acid. Non-naturally occurring amino acids include, but are not limited gto, D-amino acids, xcex2-alanine, ornithine, norleucine, norvaline, hydroxyproline, thyroxine, xcex3-amino butyric acid, homoserine, citrulline and the like. Naturally-occurring amino acids include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. Moreover, when n is greater than one, and two or more of the A groups are amino acids, then each amino acid may be independently the same or different.
When A is an invasin domain sequence, it is preferably an immune stimulatory epitope from the invasin protein of an Yersinia species described here as SEQ ID NO:77.
In one embodiment where n is 3, each A is in turn an invasin sequence (Inv), glycine and glycine.
B is optional and is a spacer comprising one or more naturally occurring or non-naturally occurring amino acids. In (B)o, where O greater than 1, each B may be same or different. B may be Gly-Gly or Pro-Pro-Xaa-Pro-Xaa-Pro (SEQ ID NO:79) or xe2x96xa1NLys or xe2x80x94NHCH (X) CH2SCH2COxe2x80x94, xe2x80x94NHCH (X) CH2SCH2CO (xe2x96xa1NLys)-, xe2x80x94NHCH (X) CH2S-succinimidyl-xe2x96xa1NLys-, and xe2x80x94NHCH (X) CH2S-(succinimidyl)-.
Th is a promiscuous T helper cell epitope selected from the group SEQ ID NOS:6, 12-19, 105, 123, 124, 20-22 and 31-35 and homologues thereof.
The peptide immunogens of this invention, may be made by chemical methods well known to the ordinarily skilled artisan. See, for example, Fields et al., Chapter 3 in Synthetic Peptides: A User""s Guide, ed. Grant, W. H. Freeman and Co., New York, N.Y., 1992, p.77. The peptides may be synthesized using the automated Merrifield solid phase peptide synthesis with either t-Boc or Fmoc to protect the xcex1-NH2 or side chain amino acids. Equipment for peptide synthesis are available commercially. One example is an Applied Biosystems Peptide Synthesizer Model 430A or 431.
After complete assembly of the desired peptide immunogen, the resin is treated according to standard procedures to cleave the peptide from the resin and de-block the functional groups on the amino acid side chains. The free peptide is purified by HPLC and characterized biochemically, for example, by amino acid analysis, by sequencing, or by mass spectometry. Methods of peptide purification and characterization are well known to one of ordinary skill in the art.
Other chemical means to generate peptide immunogens comprising the Th epitopes of the invention include the ligation of haloacetylated and cysteinylated peptides through the formation of a xe2x80x9cthioetherxe2x80x9d linkage. For example, a cysteine can be added to the C terminus of a Th-containing peptide and the thiol group of cysteine may be used to form a covalent bond to an electrophilic group such as an N chloroacetyl-modified or a maleimide-derivatized xe2x96xa1- or xe2x96xa1-NH2 group of a lysine residue, which is in turn attached to the N-terminus of a target antigenic site peptide. In this manner, Th epitope/B cell site conjugates may be obtained.
The subject immunogen may also be polymerized. Polimerization can be accomplished for example by reaction between glutaraldehyde and the xe2x80x94NH2 groups of the lysine residues using routine methodology. By another method, the linear Th/B cell site immunogen can be polymerized or co-polymerized by utilization of an additional cysteine added to the N-terminus of the linear constructs. The thiol group of the N-terminal cysteine can be used for the formation of a xe2x80x9cthioetherxe2x80x9d bond with haloacetyl-modified amino acid or a maleimide-derivatized xe2x96xa1- or xe2x96xa1-NH2 group of a lysine residue that is attached to the N-terminus of a branched poly-lysyl core molecule (e.g., K2K, K4K2K or K8K4K2K). The subject immunogen may also be polymerized as a branched structure through synthesis of the desired peptide construct directly onto a branched poly-lysyl core resin (Wang, et al., Science, 1991; 254:285-288).
The longer synthetic peptide conjugates may alternatively be synthesized by well known nucleic acid cloning techniques. Any standard manual on molecular cloning technology provides detailed protocols to produce peptides comprising the Th epitopes of the invention by expression of recombinant DNA and RNA. To construct a gene expressing a Th/target antigenic site peptide of this invention (e.g., SEQ ID NOS:36-64, 106, 71-76 and 80-82), the amino acid sequence is reverse translated into a nucleic acid sequence, preferably using optimized codons for the organism in which the gene will be expressed. Next, a gene encoding the peptide is made, typically by synthesizing overlapping oligonucleotides which encode the peptide and necessary regulatory elements. The synthetic gene is assembled and inserted into the desired expression vector. The synthetic nucleic acid sequences encompassed by this invention include those which encode the Th epitopes of the invention and peptides comprising those Th epitopes, the immunologically functional homologues thereof, and nucleic acid constructs characterized by changes in the non-coding sequences that do not alter the immunogenic properties of the peptide or Th epitope encoded thereby. The synthetic gene is inserted into a suitable cloning vector and recombinants are obtained and characterized. The Th epitopes and peptides comprising the Th epitopes are then expressed under conditions appropriate for the selected expression system and host. The Th epitope or peptide is purified and charaterized by standard methods.
Peptide immunogens of the invention may be used alone or in combination to elicit anitbody responses to Luteinizing Hormone Releasing Hormone. Luteinizing Hormone Releasing Hormone (LHRH) or Gonadotropin-releasing hormone (GnRH) is a master hormone for the regulation of sexual reproduction in both males and females. LHRH regulates the release of LH and FSH which in turn control spermatogenesis, ovulation and estrus, sexual development. LHRH ultimately controls the secretion of the male hormones andorgen and testosterone, and the secretion of the female hormones, estrogen and progesterone which themselves are essential for fertility in males and females, respectively. (Basic and Clinical Endocrinology, eds. FS Greenspan and JD Baxter, Appleton and Lange:Norwalk Conn. 1994).
Active immunization against LHRH has long been known to exert multiple effects in males including decreased serum and pituitary LH and FSH, reduced serum testosterone, suppression of spermatogenesis and reversible atrophy of the gonads and accessory sex organs. (See, for example, Fraser et al., J. Endocrinol., 1974; 63:399-405; Giri et al., Exp. Molec. Pathol., 1991; 54:255-264; Ladd et al., J. Reprod. Immunol., 1989; 15:85-101; and references cited therein). Immunization against LHRH has been proven useful as a contraceptive in males and has potential as a treatment for prostate cancer (Thau, Scand J Immunol, 1992; 36 Suppl 11:127-130; and U.S. Pat. No. 5,759,551).
Immune intervention on the hypothalo-pituitary gonadal axis by active immunization against LHRH can also be used to inhibit sexual hormones in females. Since LHRH regulates the production of FSH by the anterior pituitary which in turn regulates the production of estrogen by the ovaries, blocking the action of LHRH is a therapy for sexual hormone-dependent diseases in women. For example, the eptopic development and maintenance of endometrial tissues outside the uterine musculature is mediated by estrogen. Therefore, blocking the action of LHRH is useful as a treatment for endometriosis. Furthermore, by analogy to prostate cancer, estrogen-driven tumors of the breast should also be responsive to LHRH immunotherapy. Indeed, an anti-LHRH inducing vaccine has been shown to effectively reduce serum levels of LH and FSH in women, an illustration of the potential of this method to effect contraception and treatment of hormone-dependent disorders (Gual et al,. Fertility and Sterility, 1997; 67:404-407).
In addition to providing treatment for a number of important diseases and reversible infertility in both men and women, LHRH-based immunotherapy provides a means for reversible contraception in male and female animals (e.g. dogs, cats, horses and rabbits) as well as mitigating undesirable androgen-driven behavior such as heat, territorial marking and aggression.
Lastly, immunological castration (e.g., antibody-based inhibition of LHRH action) has application in the livestock industry. Meat from male animals is not processed into prime cuts because of the presence of an offensive aroma and taste, known as boar taint. Boar taint is conventionally eliminated by mechanical castration; however, castration of male food animals is no longer considered humane. Moreover, mechanical castration results in poorer growth performance and lesions in body part, also referred to as carcass traits, in comparison to non-castrated males. Whereas, the growth performance and carcass traits of immunocastrated animals are less affected than those of castrated animals (Bonneau et al., J Anim Sci, 1994; 72: 14-20 and U.S. Pat. No. 5,573,767). Therefore, immunological castration is preferable to mechanical castration.
LHRH (or GnRH) is a self-molecule that must be linked to a Th component in order to generate anti-LHRH antibodies (Sad et al., Immunology, 1992; 76: 599-603). Several such immunogenic forms of LHRH have been tested. For example, LHRH immunogens have been produced by conjugation to carrier proteins or linked by peptide synthesis to potent Th sites derived from pathogenic organisms (WO 94/07530, U.S. Pat. No. 5,759,551, Sad et al., 1992). Improved LHRH peptide immunogens comprising LHRH and artificial Th epitopes are exemplified in Examples 1-3.
This invention also provides for compositions comprising pharmaceutically acceptable delivery systems for the administration of the peptide immunogens. The compositions comprise an immunologically effective amount of one or more of the peptide immunogens of this invention. When so formulated, the compositions of the present invention comprising LHRH or a homologue thereof as target antigenic site, are used for treatment of prostate cancer, prevention of boar taint, immunocastration of animals, the treatment of endometriosis, breast cancer and other gynecological cancers affected by the gonadal steroid hormones, and for contraception in males and females. The utility for peptides of the invention having target antigenic sites other than LHRH will vary in accordance with the specificity of the target antigenic site.
The peptide immunogens of the invention can be formulated as immunogenic compositions using adjuvants, emulsifiers, pharmaceutically-acceptable carriers or other ingredients routinely provided in vaccine compositions. Adjuvants or emulsifiers that can be used in this invention include alum, incomplete Freund""s adjuvant (IFA), liposyn, saponin, squalene, L121, emulsigen, monophosphoryl lipid A (MPL), dimethyldioctadecylammonium bromide (DDA), QS21, and ISA 720, ISA 51, ISA 35 or ISA 206 as well as the other efficacious adjuvants and emulsifiers. Such formulations are readily determined by one of ordinary skill in the art and also include formulations for immediate release and/or for sustained release. The present vaccines can be administered by any convenient route including subcutaneous, oral, intramuscular, intraperitoneal, or other parenteral or enteral route. Similarly the immunogens can be administered in a single does or multiple doses. Immunization schedules are readily determined by the ordinarily skilled artisan.
The composition of the instant invention contains an effective amount of one or more of the peptide immunogens of the present invention and a pharmaceutically acceptable carrier. Such a composition in a suitable dosage unit form generally contains about 0.5 xcexcg to about 1 mg of the peptide immunogen per kg body weight. When delivered in multiple doses, it may be conveniently divided into an appropriate amount per dose. For example, the dose, e.g. 0.2-2.5 mg; preferably 1 mg, may be administered by injection, preferably intramuscularly. This may be followed by repeat (booster) doses. Dosage will depend on the age, weight and general health of the subject as is well known in the vaccine and therapeutic arts.
Vaccines comprising mixtures of the subject peptide immunogens, particularly mixtures comprising Th sites derived from both MVF Th, i.e., SEQ ID NOS:6, 12-19, 105, 123, 124, 20-22, and HBsAg Th, i.e., SEQ ID NOS:31-35, may provide enhanced immunoefficacy in a broader population and thus provided an improved immune response to LHRH or other target antigenic site.
The immune response to Th/LHRH peptide conjugates or other Th/target antigenic site conjugates can be improved by delivery through entrapment in or on biodegradable microparticles of the type described by O""Hagan et al. (Vaccine, 1991; 9:768). The immunogens can be encapsulated with or without an adjuvant, and such microparticles can carry an immune stimulatory adjuvant. The microparticles can also be coadministered with the peptides immunogens to potentiate immune responses
As a specific example, the invention provides a method for inducing anti-LHRH antibody by administering pharmaceutical compositions comprising Th/LHRH peptide immunogens to a mammal for a time and under conditions to produce an infertile state in the mammal. As used herein an infertile state is that state which prevents conception. Infertility can be measured by methods known in the art, e.g. evaluation of spermatogenesis or ovulation, as well as by statistical modeling of experimental animal data. Other indicators of infertility in males includes reduction of serum testosterone to castration levels and involution of the testes. The appropriate dose of the composition is about 0.5 xcexcg to about 1 mg of each peptide per kg body weight. This dosage may conveniently be divided into appropriate amounts per dose when delivered in multiple doses.
Similarly, the LHRH embodiments of this invention relate to a method for treating androgen-dependent carcinoma by administering the subject peptide compositions to the mammal for a time and under conditions to prevent further growth of the carcinoma. The appropriate unit dose is about 0.5 xcexcg to about 1 mg of each peptide per kg body weight. This is conveniently divided into the appropriate amounts per application when administered in multiple doses.
Further, the LHRH embodiments relate to a method for improving the organoleptic qualities and tenderness of the meat from male domestic animals while maintaining the advantageous growth performance of intact males. The androgenic steroid hormones of intact males are responsible for fast growth but their presence is accompanied by non-androgenic steroids (e.g., 5xcex1androstenone) and skatole (a product of the microbial metabolism of tryptophan) which impart unpleasant taste and aroma to the meat. This condition, known as boar taint in the case of swine, detracts from the quality of the meat. However, by the active immunization of young males with compositions comprising LHRH peptides of the invention, on a schedule that effects immunocastration in the weeks just prior to slaughter, many of the growth advantages of non-castrated males may be retained while providing meat with improved flavor and tenderness.
The efficacy of the peptide composition of the present invention comprising the target antigenic site, LHRH, can be tested by the procedure described in the Examples 1-3.
Other target antigenic sites which have also been used in peptide immunogens of the present invention are described in Examples 4-9. Peptide immunogen compositions are useful for inducing immune responses in mammals against specific target antigens and provide for prevention or treatment of disease, or intervene to usefully modify normal physiological conditions.